Poultry and other animal waterers are used in ambient outdoor temperatures or in coops, sheds, shelters, or barns in which the ambient temperature may be near or below the freezing point of water (i.e., in sub-freezing conditions) or be above a desirable temperature in hot conditions. In cold weather, some watering dishes or troughs are provided with external heaters (e.g., an electrical resistance heater) or immersion heaters. Such waterers are susceptible to fouling by animal wastes, and in sub-freezing temperatures, may consume substantial and costly power to prevent the water from freezing.